Casting of magnesium and its alloys



Feb. 16, 1937. F. BADGER CASTING OF MAGNESIUM AND ITS ALLOYS V w w Filed Nov. 22, 1934 Patented Feb. 16, 1937 PATENT OFFICE CASTING OF MAGNESIUM AND ITS ALLOYS Frederick Badger, Point Pleasant, Wandsworth,

London, England, assignor to Magnesium Castings and Products Great Britain Limited, Slough, Bucks,

Application November 22, 1934, Serial No. 754,345

In Great Britain 1 Claim.

In the casting of magnesium and of its alloys great difilculty is experienced in obtaining clean flawless castings. This is due partly to the highly oxidizable nature of the metal itself and partly to the fluxes used since it is difllcult to avoid the accidental inclusion of small quantities of these oxides and fluxes during the process of pouring. In addition the oxidation which occurs to some extent during the pouring of the metal creates impurities which are carried with the metal into the mould. This causes defects in the casting and renders the metal particularly liable to attack near the gates of the mould.

Attempts have been made to avoid these defects and overcome the previously described dlfflculties by subdividing the stream of metal immediately prior to its entry in the casting space, for instance by means of a perforated plug of refractory material, for example as in my British Patent 375, 979.

Said method has given satisfactory results when employed for making smaller castings but is not always so eflicient when applied to castings of large size.

Large and intricate castings generally necessitate the use of runners of considerable depth and also frequently the use of sand cups on the top of the mould, thus further increasing the head of the metal. It has been found in practice that a large volume of metal under a considerable head in falling from its point of entry at the top of the mould to the perforated plug located near the bottom of the mould induces considerable turbulence on the face of the plug with the formation of oxide skin. At the same time the pressure exerted by the metal is sufficient to force particles of the oxide skin through the perforations. least partly neutralized and lost, thereby.

The present invention has for its object the provision of a way for overcoming this particular dimculty and consists in subdividing. the stream of molten metal not in a single levelof the runner but in a plurality of levels located at different heights, for instance by providing several perforated plugs in one or each runner. Under such conditions, the head of metal bearing upon the The useful effect of said plugs is thus at November 22, 1933 (Cl. 22l34) ever, the number and size of the perforations of said plugs will generally be determined in such a way that the area ofiered to the passage of the metal is larger in the higher than in the lower plug, whereby the space intermediate said plugs will be kept .filled with molten metal, after the early part of the pouring operation.

(11) The number of plugs provided in a runner may under certain conditions exceed two.

In all cases, the provision of one or more upper plugs reduces the rate of flow of the molten metal falling upon the lower plug and enables one to secure in the pouring of large castings the same advantages as those obtained with a single plug in making small castings. The stream of metal descending from the upper plug falls on to the lower plug with considerably less force and leaves a greater proportion of the inclusions of flux and oxide skin on the upper plug. Finally the metal enters the mould through the second plug at,a steady controlled rate and without turbulence, free from the previously mentioned inclusions.

The annexed drawing shows apparatus in which the process of the present case can conveniently be carried out, this being given purely by way of example and without restricting the invention to the use of this apparatus.

Fig. 1 represents a vertical section of the apparatus and Fig. 2 a top plan view of the same.

In said drawing l represents the lower portion of the space in the mold, 2 represents a suitable metallic casing surrounding the mold, 3 represents a core, 4 and 5 represent vertical extension of the space I.

6 is the upper strainer referred to above, which is positioned above the lower strainer 1. Both 6 and l are perforated as shown, and constituteperforated plugs. as mentioned above.

The molten magnesium is poured into the space above the plug 6, and the magnesium in molten condition is again strained through the perforations in the plug 1, and enters the hollow space I of the mold at near the bottom.

Having now particularly described and ascertained the nature of my invention and in what manner the same is to be performed, I declare that what I claim is:

A mold for casting metallic magnesium and its alloys, having a mold cavity and a runner leading to the lower part of said mold cavity, and a plurality of foraminous plugs in said runner, located at different levels in the height thereof, the penultimate plug having a larger free area for the passage of molten metal than the last plug.

FREDERICK BADGER. 

